1. Field of the Invention
The present invention relates to a member for electrophotography, a process cartridge, and an electrophotographic image forming apparatus.
2. Description of the Related Art
A developing method involving using a nonmagnetic one-component toner has been known as the image forming method of an electrophotographic image forming apparatus, such as a copying machine or an optical printer. Specifically, a photosensitive member serving as a rotatable electrostatic latent image-bearing member is charged by a charging unit, such as a charging roller, and an electrostatic latent image is formed by exposing the surface of the charged photosensitive member to laser light. Next, in the developing apparatus of the image forming apparatus, a toner in a developer container is applied onto a developing roller by a developer-regulating member, and the electrostatic latent image is developed with the toner at a contact portion between the photosensitive member and the developing roller. After that, the toner image on the photosensitive member is transferred onto a recording material through or without through an intermediate transfer member in a transferring portion, the toner image is fixed onto the recording material by heat and pressure in a fixing portion, and the recording material having the fixed image is discharged to the outside of the image forming apparatus.
In such image forming method, the developing apparatus includes such members for electrophotography as described below:
(1) a developer-supplying roller present in the developer container and configured to supply the toner to the developing roller;
(2) the developer-regulating member configured to form a toner layer on the developing roller and to keep the amount of the toner on the developing roller constant; and
(3) the developing roller configured to develop the toner on the photosensitive member, the roller being arranged so that the roller closes the opening of the developer container storing the toner, part of the roller is exposed to the outside of the container, and the exposed portion faces the photosensitive member.
In the developing apparatus, image formation is performed by the rotation and rubbing of those members for electrophotography.
A reduction in size of the apparatus and the energy savings thereof have been advancing in recent years. One method for the reduction in size of the apparatus is a reduction in diameter of any such member for electrophotography. In addition, one method for the energy savings is a reduction in torque (a reduction in penetration amount of any such member or a reduction in peripheral speed difference between the members) at the time of the rotation and rubbing of the members for electrophotography. However, when the reduction in torque at the time of the rotation is performed by reductions in diameters of the developing roller and the developer-supplying roller, or the reduction in penetration amount of any such member or the reduction in peripheral speed difference between the members, the amount of the toner layer to be formed on the developing roller becomes insufficient and hence a uniform image is not obtained in some cases.
In Japanese Patent Application Laid-Open No. H08-286497, there is a disclosure of the following developing roller. In order to improve the toner-conveying force of a developing member, a dielectric portion having a high electric resistance value is arranged on the surface of the roller, and the charged dielectric portion is caused to electrically adsorb a toner, thereby enabling the conveyance of the toner.
The present invention is directed to providing a member for electrophotography that can achieve both an improvement in toner-conveying force under high temperature and high humidity, and excellent charge-providing performance for a toner, at high levels. In addition, the present invention is directed to providing a process cartridge and an electrophotographic image forming apparatus that can stably provide high-quality electrophotographic images under various environments.